Joining techniques in the timber trades date back to pre history and little in the form of timber joinery has not been explored or tried in one form or another. However, the more complex or demanding a joinery technique is to execute, in particular in an industrial or reproducible and economical fashion, the more likely it is that such a technique should be avoided for the obvious reasons of cost and efficiency.
Furthermore, industrial standards of accuracy and reproductability are very demanding and can rarely tolerate the vagaries associated with hand built joinery and/or the intricacies often practiced by experienced craftspeople.
The development of improved tools, in particular high speed power tools and machines has expanded the scope of joinery techniques available to industry and the general public. The hand held router for example, has revolutionized joinery for the general public, such that wood joinery techniques which were previously only able to be executed by experienced practitioners can be routinely used by virtually any operator of a hand held router.
Industry also makes extensive use of routers from simple hand held units familiar to the home handyman through a highly complex computer controlled multihead machines. In addition to the router, industry makes extensive use of the larger and more powerful shaper. The shaper can be considered a heavy duty version of the router, albeit utilizing a very different type mounting method for the cutters. The use of both routers and shapers in industry has lead to an ever increasing level of sophistication in the development of wood joining techniques used by industry.
The age old joining technique of dovetailing, which was traditionally used for the joining of drawer and carcass elements in furniture has experienced a colossal increase in application with the assistance of routers where dovetail shaped grooves can be easily made through a piece of timber to provide tapered slots. Such tapered slots can be used in co-operation with complimentary splines to provide a method of joining long lengths of timber together in a self locking joint which can be used as an edge-join, surface-join, end-join or any combination of the above.
The use of dovetails in the above method of joinery is very versatile; however, the configuration of the cutter used to produce a dovetail shaped slot in one pass requires the cutter to have wings extended beyond the width of the neck region of the cut so as to provide an undercut or inverted tapered slot expanding in width away from the face surface of the stock. This shape, which is necessary to allow the cutter to make the undercut dovetail slot in a single pass precludes the insertion or removal of the cutter at any point intermediate along the length of the effective cut. The cutter must be inserted into the stock, at the full depth of cut, at the beginning of the cut and remain fully within the cut until the very end of the cut.
Accordingly, dovetailed slots cut with a router must be cut at full depth for the whole length of the effective cut and cannot be plunged into or out of the stock intermediate of the cut.
Furthermore, a router cutter has a very small radius of cut which imposes limitations on the final quality of the cut surface. The routers very high speed partially compensates for this, but only if very sharp cutters are always used. The shaper, on the other hand, has a much greater radius of cut due to the positioning of the cutter knives at a chord across the rotating cutter head rather than axially in line with the rotating head as in the router. However, the shaper cutters are only capable of entering into stock at an angle normal to the axis of rotation of the cutters, unlike a router which can also enter stock in a direction axial to the cutter. Accordingly shaper cutters are not normally able to take cuts which involve any undercutting into the stock which characterize the dovetail joint.
The limitations in preparing dovetailed cuts with both routers and shapers as discussed above has restricted the use of this joinery technique, particularly in industry, to date. It would be very desirable if such dovetail shaped cuts could be made utilizing the benefit of the shaper, namely speed, accuracy, repeatability, low cost per linear meter and application to mass production.